Such an initialisation protocol is already known in the art, e.g. from the communication between two Asymmetric Digital Subscriber Line (ADSL) modems operating in accordance with the specifications of the ANSI (American National Standards Institute, Inc.) Standard on ADSL, the approved version of which has the reference T1E1.413 and title "Network and Customer Installation Interfaces, Asymmetric Digital Subscriber Line (ADSL) Metallic Interface". In the draft version of this standard published in April 1994, the initialisation protocol to be executed by an ADSL transceiver pair interconnected via a communication link, e.g. a twisted pair copper telephone line, is described in chapter 12, from page 83 to page 104. In view of the present invention, only a part of this initialisation protocol is relevant. More particularly, the part wherein the two communicating ADSL transceivers negotiate the future upstream and downstream data rates is to be considered. In FIG. 29 on page 83 of the above cited draft Standard Specification, this part is indicated by "Channel Analysis" and "Exchange"; The "Channel Analysis" procedure contains a first phase wherein the first ADSL transceiver, named the central office modem, transmits four optional upstream and downstream data rate values to the second ADSL transceiver, named the remote terminal modem. The second ADSL transceiver replies upon receipt of the just mentioned proposal by transmitting four optional upstream data rate values to the central office modem. These optional data rate values sent from transceiver 1 to transceiver 2 and vice versa, from transmitter 2 to transmitter 1, are encapsulated in the so called C-RATES1 and R-RATES1 messages described in paragraph 12.6.2 on pages 92-93 and 12.7.4 on page 96 of the above mentioned draft Standard Specification respectively. The "Exchange" procedure in addition contains a third phase wherein the central office modem and remote terminal modem communicate to each other which one of the optional data rates they prefer to use. In a fourth phase which also forms part of the "Exchange" procedure of the ADSL initialisation protocol, the remote terminal modem transmits a so called R-B&G message to the central office modem. This message contains the bits and gains information for the carriers which will carry the discrete multi tone (DMT) symbols that will constitute the future communication between the ADSL transceivers. This bits and gains information can be seen as a confirmation of the selected data rate in the previous phase, since the downstream and upstream data rates for future transmission are completely determined thereby. A disadvantage of the above known initialisation protocol is that the final selected and confirmed upstream and downstream data rates can not differ from the four data rate values proposed in the first phase. These proposed data rate values are chosen rather arbitrarily and may all differ significantly from the optimal upstream and downstream data rates which depend on the communication link characteristics. In other words, the known initialisation protocol does not support adaptive data rates, i.e. data rates which are adapted to the capacity of the communication link between the two transceivers. The only way to adapt data rates is to restart the complete identification and initialisation process.